The solar cell industry is recently one of the most popular energy technology industries. In the solar cell industry, researchers and developers constantly seek for enhanced photoelectrical conversion efficiency. To prevent a light receiving surface of a solar cell from being disposed with an excessive number of elements and thus reducing an area from illumination of a light source, a backside contact solar cell is developed. In a backside contact solar cell, all electrodes are manufactured on a back side of a substrate opposite to the light receiving surface, so as to prevent reduction of illuminated area and to enhance overall photoelectric conversion efficiency.
In the U.S. Pat. No. 7,135,350 disclosing “Use of Doped. Silicon Dioxide in the Fabrication of Solar Cells”, silicon oxide containing impurities is utilized as a diffusion source. After depositing silicon oxide containing a first impurity, a layer of pure silicon oxide is covered thereupon. Silicon oxide containing a second impurity is then deposited thereupon after patterning, and a layer of pure silicon oxide is covered again to eventually form a PN junction plane at a back side after high-temperature diffusion. However, in the fabrication process above, two lithography etching processes are required. Thus, in addition to being suitable for only growing monocrystalline silicon, the above fabrication process also involves complicated manufacturing steps and stricter manufacturing conditions. As such, the fabrication process is quite high in cost and falls short in meeting a low cost appeal of solar cells.
In the U.S. Pat. No. 7,633,006 disclosing “Back Side Contact Solar Cell with Doped Polysilicon Regions”, a first diffusion source is fabricated on a surface of a polycrystalline silicon by low pressure chemical vapor deposition (LPCVD); after the first diffusion source is covered by a patterned oxidized layer, a second diffusion source is then fabricated. After high-temperature diffusion, impurities enter the polycrystalline silicon to form a PN junction plane. The low pressure chemical vapor deposition needs to be performed under a high temperature of 600 to 700 degrees Celsius at higher costs. Further, safety concerns are also brought if the low pressure chemical vapor deposition process involves hazardous gases such as SiH4 and H2.